aio-libs/aiohttp · error · ContentEncodingError

deflate

Error message

deflate

What it means

ContentEncodingError('deflate') raised in DeflateBuffer.feed_eof when, after consuming all input for a deflate-encoded body, the zlib decompressor reports it has not reached end-of-stream (decompressor.eof is False). This indicates the deflate stream is incomplete/truncated.

Source

Thrown at aiohttp/http_parser.py:1207

            raise ContentEncodingError(
                "Can not decode content-encoding: %s" % self.encoding
            )

        if chunk:
            self.out.feed_data(chunk)
        return self.decompressor.data_available

    def feed_eof(self) -> None:
        chunk = self.decompressor.flush()
        # This should never contain data as we defer the call until exhausting
        # the decompression. If .flush() is returning data, this may indicate a
        # zip bomb vulnerability as it will decompress all remaining data at once.
        assert not chunk

        if self.size > 0:
            # decompressor is not brotli unless encoding is "br"
            if self.encoding == "deflate" and not self.decompressor.eof:  # type: ignore[union-attr]
                raise ContentEncodingError("deflate")

        self.out.feed_eof()

    def begin_http_chunk_receiving(self) -> None:
        self.out.begin_http_chunk_receiving()

    def end_http_chunk_receiving(self) -> None:
        self.out.end_http_chunk_receiving()


HttpRequestParserPy = HttpRequestParser
HttpResponseParserPy = HttpResponseParser
RawRequestMessagePy = RawRequestMessage
RawResponseMessagePy = RawResponseMessage

with suppress(ImportError):
    if not NO_EXTENSIONS:
        from ._http_parser import (  # type: ignore[import-not-found,no-redef]

View on GitHub (pinned to c0ef574e29)

Solutions

1. Confirm the full deflate stream was delivered (compare against curl --compressed).
2. Check for truncation by the server/proxy.
3. Retry; handle as a transport error.
4. Use Accept-Encoding: identity to bypass if upstream is consistently broken.

from aiohttp.http_exceptions import ContentEncodingError
try:
    body = await resp.read()
except ContentEncodingError:
    # truncated deflate — retry or request identity
    ...

When it happens

Trigger: On EOF for a deflate body, if size > 0 and `not self.decompressor.eof`, the stream didn't finish cleanly — truncated deflate payload. feed_eof raises ContentEncodingError('deflate').

Common situations: Truncated gzip/deflate download; server closing the connection before flushing the final deflate block; proxy truncation; miscomputed Content-Length on a compressed body.

Related errors

• Can not decode content-encoding: brotli (br). Please install
• Can not decode content-encoding: zstandard (zstd). Please in
• Can not decode content-encoding: %s
• Invalid window size
• Extension for deflate not supported{ext}

AI-assisted analysis of aio-libs/aiohttp@c0ef574e29 (2026-08-04). Data as JSON: /data/errors/4b5f1fc1ef80dc88.json. Report an issue: GitHub.